1. Genetics is the study of how traits are passed from parents to offspring through chromosomes and genes. Chromosomes contain genes that determine traits and are located in cell nuclei. 2. Body cells contain pairs of chromosomes while sex cells like eggs and sperm only contain half the number to allow for chromosome pairing during fertilization. 3. Traits are passed to offspring when the chromosomes from the mother and father combine during fertilization. Dominant genes mask recessive genes, determining whether traits are expressed.